The present invention relates to a method for producing a soot sensor and to a soot sensor produced according to such a method.
Soot sensors are used to control or regulate the combustion process of engines, in particular of diesel engines and oil heaters. Depending on the quantity of soot particles, the combustion may be controlled such that fewer soot particles occur and/or combustion is more efficient.
DE 10 2007 038 680 A1 discloses a soot sensor in which a conductive track structure is applied on a smooth Al2O3 surface. Such a structure simplifies the adsorption of soot particles.
From WO 2011/106625 A1, a soot sensor is known which is designed with a heating element and a sensor element on a substrate. The electrical resistance between the heating element and the sensor element changes if soot particles settle on the surface of the soot sensor. It is therefore possible to determine the concentration of soot particles on the surface and, therefore, in the flow of exhaust gas. The heating element is heated to a sufficiently high temperature in order to burn free the sensor.
Additional sensors may also be used to control the combustion process, such as lambda probes or temperature sensors, for example. Continuously increasing requirements regarding the reduction of soot emissions are demanded on soot sensors for controlling diesel engines. For example, the so-called EU6 Guideline requires that vehicles operated by diesel engines have very low quantities of soot. Such low soot quantities are very difficult to detect using the known soot sensors due to the low number of soot particles; i.e., due to the very low concentration of soot particles in the flow of exhaust gas.
The disadvantage of the known soot sensors, therefore, is that such soot sensors do not react with sufficient sensitivity to be capable of meeting the increasingly stricter requirements. Another disadvantage of the known sensors is that a large number of sensors must be installed in the flow of exhaust gas, such that a large number of connecting terminals is required. At the same time, however, there is always a desire to produce the engines or the combustion systems in a manner that is as simple and as cost effective as possible. The sensors themselves should also be as cost effective as possible. Furthermore, the sensors should be robust and error-free when installed in the exhaust gas system.